Method for transmitting a response request frame and a response frame in a multi-user based wireless communication system

ABSTRACT

The present invention relates to a method for efficient transmission of a request frame such as an RTS/CTS frame and a response frame in response to the request frame in a multi-user based wireless communication system. The method of the present invention comprises: a process where wireless terminals transmit a response frame at their own response frame transmission time through a request frame that contains information about a plurality of wireless terminals and information about the response frame transmission time of the respective wireless terminals; a process where the respective wireless terminals transmit a response frame according to a token scheme such that the response frame is transmitted to a final access point; and a process where only a representative wireless terminal selected depending on a given wireless environment receives the response frame.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of the U.S. patent applicationSer. No. 13/479,218, filed on May 23, 2012, which is a By-passcontinuation Patent Application No. PCT/KR2010/008362, filed on Nov. 24,2010, which claims priority to Korean Patent Application10-2009-0113916, filed on Nov. 24, 2009, which are incorporated byreference in their entirety.

TECHNICAL FIELD

Exemplary embodiments of the present invention relate to a method fortransmitting a response request frame and a response frame in a wirelesscommunication system, and more particularly, to a method for effectivelytransmitting a request frame such as a Request to Send/Clear to Sendframe (RTS/CTS) and a response frame thereof in a multi-user wirelesscommunication system.

BACKGROUND ART

A wireless local area network (WLAN) basically supports an access point(AP) for a distributed system (DS) and a basic service set (BSS) formedof a plurality of stations (STA).

A Medium Access Control (MAC) protocol of a WLAN operates based on acarrier sense multiple access/collision avoidance (CSMA/CA).Accordingly, a WLAN may waste resources in channel competition. In orderto overcome such a problem, an enhanced MAC protocol defined in IEEE802.11 (e) introduced a burst transmission scheme. The bursttransmission scheme transmits multiple MPDUs with a short inter-framespace (SIFS) during a transmission opportunity time (TXOP) when atransmission right for a wireless resource is obtained. Further, theburst transmission scheme receives a Block ACK frame in response to themultiple MPDUs.

Further, IEEE 802.11(n) defines an Aggregated MSDU (A-MSDU) scheme andan Aggregated MPDU (A-MPDU) scheme. The Aggregated MSDU (A-MSDU) schemepacks multiple MSDUs together into an A-MSDU and transported within asingle MPDU and the Aggregated MPDU (A-MPDU) scheme packs multiple MPDUstogether into an A-MPDU and transported as a single transmission unit inorder to reduce overhead such as SIFS intervals. In general, a minimumSIFS interval is maintained when MPDUs are individually transmitted.

Lately, users for a WLAN have been abruptly increased. In order toincrease data throughput provided from one BSS, IEEE 802.11 (ac) hasbeen developing a standard for a very high throughput (VHT) WLAN system.

The VHT WLAN system is capable of supporting a maximum throughput of1Gbps for MAC SAP of an access point in three multiple stationsenvironments including one access point (AP) and two stations (STA) andsupporting a maximum throughput of 500 Mbps for MAC SAP of a wirelessstation in point-to-point environment. Each access point (AP) andstation of a VHT WLAN are designed to support comparability to anexisting WLAN system (IEEE 802.11a/n).

A wireless station obtaining a transmission opportunity is required toreceive response through an ACK frame or a response frame in response toa transmitted frame in order to enhance reliability of wirelesscommunication in a wireless communication system such as WLAN.

Such response includes an immediate response and a delayed response. Theimmediate response is a response (ACK frame) for single data. The blockresponse for successive transmission or an aggregated MPDU correspondsto both of the immediate response and the delayed response.

The immediate response is to transmit a response frame with a short timeinterval such as a short inter-frame space (SIFS) whenPHY-RXEND.primitive is generated for a received request frame in orderto prevent other stations from transmitting data. As described above, arequest and response frame exchange sequence is performed as a pair.Here, the immediate response frame such as an ACK frame or a CTS framemay not include a transmission address.

Unlike the immediate response, the delayed response transmits an ACKframe at first as a basic response that informs whether a request hasbeen received or not and transmits a response frame including requestedinformation later. The response frame is transmitted through an enhanceddistributed channel access (EDCA) or based on a piggyback scheme withother frame. In the delayed response, a transmitting station receiving aresponse frame from a receiving station informs the receiving stationwhether a response frame has been received or not through an ACK frameagain.

As described above, the request and response frame exchange sequence ina WLAN may be adapted at a multi-user wireless communication system. Incase of supporting a multi-user multiple input multiple output (MU-MIMO)technology for uplink, wireless stations receiving frames may transmitresponse frames at the same time after a predetermined interval (IFS)between frames according to the frame exchange sequence.

Meanwhile, a wireless station receiving a frame is required to transmita response frame with a time interval or using different channels forbetter throughput regardless of supporting the MU-MIMO technology foruplink.

A method for exchanging frames with a time interval and using a samebandwidth in a WLAN system includes a method for exchanging a responserequest frame and a response frame through channel access by a wirelessstation, and a method for sequentially transmitting a response frame ata plurality of wireless stations through one request frame.

That is, in the method for exchanging a request frame and a responseframe through channel access by a wireless station, an access point (AP)transmits a request frame to a first wireless station through channelaccess and the first wireless station transmits a response frame with ashort time interval such as SIFS. Then, the access point (AP) transmitsa request frame to a second wireless station through second channelaccess and the second wireless station transmits a response frame with ashort time interval such as SIFS.

In the method for sequentially transmitting response frames at aplurality of wireless stations through one request frame, one requestframe including information on addresses of multiple users istransmitted through channel access. Then, a plurality of terminalssequentially transmits response frames with a short inter-frame space inresponse to the request frame.

Such a related request and response frame exchange sequence is performedafter deciding a transmitting station and a receiving station, and therequest frame and the response frame are exchanged with a short timeinterval such as SIFS in order to prevent other wireless station fromobtaining a transmission right.

However, there has been a demand for developing a method for exchanginga request frame and a response frame effectively although a responseframe does not include information on an address of a transmittingstation like an ACK frame for a data frame or like a CTS frame for a RTSframe in a MU-MIMO wireless communication environment.

DISCLOSURE Technical Problem

An embodiment of the present invention is directed to a method fortransmitting a request frame and a response frame in order toeffectively exchange a request frame and a response frame in amulti-user multiple input multiple output (MU-MIMO) wirelesscommunication system.

Other objects and advantages of the present invention can be understoodby the following description, and become apparent with reference to theembodiments of the present invention. Also, it is obvious to thoseskilled in the art to which the present invention pertains that theobjects and advantages of the present invention can be realized by themeans as claimed and combinations thereof.

Technical Solution

An embodiment of the present invention provides a method fortransmitting a response frame at a corresponding response frametransmission time at each wireless station through a request framehaving information on a plurality of wireless stations and informationon a response frame transmission time of each wireless station.

That is, the method for transmitting a request frame requesting aresponse to a plurality of wireless stations in a multi-user multipleinput multiple output (MU-MIMO) wireless communication system, includes:generating the request frame having an indicator for informing thatthere are a plurality of wireless stations to receive a frame andmulti-user information on the plurality of wireless stations; andtransmitting the generated request frame. The multi-user information mayinclude multi-user identifier (ID) information and response frametransmission time information of each wireless station.

Also, a method for transmitting a request frame requesting a response toa plurality of wireless stations in a MU-MIMO wireless communicationsystem, includes: receiving the request frame having an indicator andmulti-user information, wherein the indicator indicates presence of aplurality of wireless stations receiving a frame and the multi-userinformation is information on the plurality of wireless stations; andtransmitting a response frame at a corresponding response frametransmission time based on the multi-user information included in therequest frame.

The response frame transmission time information may be informationabout response frame transmission times of wireless stations, and aresponse frame transmission time of a predetermined wireless station maybe decided based on a sum of duration for transmitting previous responseframes and intervals between the previous response frames, wherein theprevious response frames are response frames transmitted before thepredetermined wireless station.

Another embodiment of the present invention provides a method fortransmitting a response frame to a final access point by transmitting aresponse frame based on a token scheme at each wireless station.

That is, a method for transmitting a request frame requesting a responseframe to a plurality of wireless stations in a MU-MIMO wirelesscommunication system, includes: generating the request frame having anext multi-user identifier list and a token after setting up wirelessstation information as a receiving station address, wherein the networkmulti-user identifier is information on wireless stations that do nottransmit the response frame among a plurality of wireless station, thetoken is reduced according to transmission of a response frame, and thewireless station information is information on a wireless station totransmit a next response frame; and transmitting the generated requestframe.

Also, a method for transmitting a request frame requesting a responseframe to a plurality of wireless stations in a MU-MIMO wirelesscommunication system, includes: receiving the request frame having anext multi-user identifier list and a token, wherein the next multi-useridentifier list is information on wireless stations that do not transmitthe response frame and the token is reduced according to transmission ofa response frame; and transmitting a response frame reconfigured bysetting up one of identifiers in the next multi-user identifier list,reducing the token, and excluding the identifier setup as the address ofthe receiving station.

When all multi-user identifiers included in the next multi-useridentifier list are set up as an address of a receiving station, thenext multi-user identifier may be set up as ‘null’.

A wireless station receiving the next multi-user identifier setup as‘null’ and the token setup as ‘0’ may transmit the response frame bysetting up an address of a receiving station for the response frame asan address of an access point.

When a predetermined wireless station fails to transmit the responseframe, a wireless station transmitting a response frame by setting up anaddress of a receiving station as the predetermined wireless station maytransmit a response frame to other wireless station included in the nextmulti-user identifier list.

The predetermined wireless station failed may receive a request framefrom an access point and may transmit a response frame.

After the predetermined wireless station receives a response frame fromother wireless station, the predetermined wireless station may transmita response frame by setting up an address of a receiving station as anaddress of an access point.

Yet another embodiment of the present invention provides a method forreceiving a response frame only for a representative wireless stationdecided according to wireless environment.

That is, a method for transmitting a request frame requesting a responseto a plurality of wireless stations in a MU-MIMO wireless communicationsystem includes: selecting a representative wireless station to transmita response frame from a plurality of stations according to wirelessenvironment such as a channel quality; and transmitting a request frameby setting up an address of a receiving station based on information onthe selected representative wireless station.

The request frame may further include information on the number ofmulti-user stations and multi-user identifiers.

When it is failed to receive a response frame from the representativewireless station, an access point may transmit a request frame bysetting up other wireless station as a representative wireless stationto transmit a response frame according to the wireless environment.

When it is failed to receive a response frame from the selectedrepresentative wireless station, an access point may retransmit arequest frame to the selected representative wireless station.

Advantageous Effects

In accordance with embodiments of the present invention, it is possibleto effectively exchange a request frame and a response frame although aresponse frame does not include an address of a transmitting stationlike an ACK frame for a data frame or like a CTS frame for a RTS framein a MU-MIMO wireless communication system. Accordingly, a wirelessservice performance provided to a user is improved, and a powermanagement function and a comparability function can be applied.

DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating a structure of a frame includingmulti-user information where the present invention is applied.

FIG. 2 is a diagram illustrating a structure of multi-user informationusing a response frame transmission time in accordance with a firstembodiment of the present invention.

FIGS. 3 and 4 illustrate a structure of multi-user information using atoken scheme in accordance with a second embodiment of the presentinvention.

FIG. 5 is a diagram illustrating a method for transmitting a responseframe using a token scheme in accordance with an embodiment of thepresent invention.

FIGS. 6 and 7 are diagrams illustrating a recovering method according totransmission failure of a response frame in a token scheme in accordancewith an embodiment of the present invention.

FIGS. 8 and 9 are diagrams illustrating a method for transmitting aresponse frame using a representative wireless station in accordancewith a third embodiment of the present invention.

BEST MODE

Exemplary embodiments of the present invention will be described belowin more detail with reference to the accompanying drawings. The presentinvention may, however, be embodied in different forms and should not beconstrued as limited to the embodiments set forth herein. Rather, theseembodiments are provided so that this disclosure will be thorough andcomplete, and will fully convey the scope of the present invention tothose skilled in the art. Throughout the disclosure, like referencenumerals refer to like parts throughout the various figures andembodiments of the present invention. The drawings are not necessarilyto scale and in some instances, proportions may have been exaggerated inorder to clearly illustrate features of the embodiments.

Hereinafter, a method for transmitting a request frame and a responseframe according to embodiments of the present invention will bedescribed based on a multi-user multiple input multiple output (MU-MIMO)wireless communication system defined in IEEE 802.11 among various highspeed wireless communication systems. However, the embodiments of thepresent invention are not limited thereto. The method for transmitting arequest frame and a response frame according to embodiments of thepresent invention may be applied to any wireless communicationenvironments using a multi-channel technology or a multi-user multipleinput multiple output (MU-MIMO) technology.

FIG. 1 is a diagram illustrating a structure of a frame includingmulti-user information where the present invention is applied to.

A frame control field includes a protocol field for indicating aprotocol version such as an IEEE 802.11 MAC version, a type field or asubtype field for identifying a type of a frame in use, and additionalfields for carrying various parameters to control a frame, such as aToDS field, a FromDS field, an additional fragment field, a retry field,a power control field, an additional data field, a WEP field, and anorder field.

A Duration field is used to set a network allocation vector. As theduration field of the present embodiment, a duration field included in aframe transmitted during a contention free period (CFP) or in a PS-Pollframe is used.

A sequence control field is used to discard afragmentation/defragmentation frame or a duplicate frame. The sequencecontrol information includes a 4-bits fragmentation number field and a12-bit sequence number field.

The frame body field is a typical data field. The frame body fieldincludes a payload. A frame check sequence (FCS) is used for integritycheck of a frame received from a predetermined station.

As described above, a MAC frame essentially includes the frame controlfield, the duration field, a receiving address (RA) field, and a FCSfield. The remaining fields may be excluded or added according to a typeof a frame for saving wireless resources. For example, a QoS controlfield may be excluded in case of a data frame not using QoS. In case ofan IEEE 802.11n dedicated frame, a HT control field is additionallyincluded for a HT function as well as the QoS control field.

The frame control information may be analyzed by all stations in orderto detect a type of a received frame. The duration information may beanalyzed by all stations to prevent collision between frames on awireless medium. The receiving address may be analyzed by all stationsfor determining whether a destination address of a received frame is anown address or not. When the destination address of the received frameis the own address, the receiving station decodes the remaininginformation of the received frame.

In order to include information on a plurality of receiving stations ina frame, it is required to include an indicator in one of fields thatcan be analyzed by all stations. Such an indicator may indicate that aframe having information on a plurality of receiving stations. Further,multi-user information is additionally included in the frame. Referringto FIG. 1, a predetermined bit in the frame control field or thereceiving address (RA) field may be used as the indicator that indicatesthat a frame includes multi-user information.

In a general method for responding a frame requiring an immediateresponse, a response frame is transmitted with a short time intervalsuch as SIFS after receiving a request frame as described above.However, when the request frame requiring the immediate responseincludes the multi-user information, response frames may be collidedbecause a plurality of stations transmits the response frames at thesame time. In order to overcome such a problem, a method forsequentially transmitting response frames at a plurality of stations wasintroduced.

FIG. 2 is a diagram illustrating a frame including multi-userinformation in accordance with a first embodiment of the presentinvention. That is, the frame of FIG. 2 has a format for sequentiallytransmitting a response frame at a corresponding transmission time at aplurality of wireless stations.

Referring to FIG. 2, a multi-user information field includes multi-useridentifier (ID) information and response frame transmission timeinformation. The response frame transmission time information denotes atime of transmitting a response frame corresponding to each user. Themulti-user identifier (ID) information denotes a unique value of awireless station such as a MAC address or an Association ID. Theresponse frame transmission time for a k^(th) user may be decided by asum of duration TX_RSP_DURk-1 for transmitting response frames of afirst user to a (k−1)^(th) user and short inter-frame spaces (SIFS)therebetween.

In case of a first embodiment of the present invention, a transmittingstation includes the multi-user information with the response frametransmission time information in a request frame and transmits therequest frame to a plurality of receiving stations. Accordingly, eachreceiving station transmits a response frame at a corresponding responseframe transmission time to a transmitting station.

Hereinafter, a method for sequentially transmitting response frames at aplurality of stations in accordance with a second embodiment of thepresent invention will be described.

In the second embodiment of the present invention, a token scheme isused. In the token scheme, a multi-user request frame includesinformation on the number of user stations transmitting a response frameand user station IDs. Response frames are sequentially transmitted bytransmitting the multi-user request frame.

FIGS. 3 and 4 illustrate a structure of multi-user information in atoken scheme in accordance with an embodiment of the present invention.

Referring to FIG. 3, the multi-user information includes the number oftokens and a next multi-user ID list for transmitting a next responseframe. In case of using the token scheme according to the secondembodiment of the present invention, a transmitting station transmittinga request frame records information on an ID of a wireless station totransmit a response frame with a short inter-frame space (SIFS) amongmultiple users in a receiving address (RA) field, sets up a token valuedenoting the number of multiple users to transmit a response frame,forms a next multi-user ID list for multiple users except the currentreceiving station, and transmits a request frame.

Referring to FIG. 4, a wireless station receiving a request framereduces a token number by ‘1’ after a short inter-frame space (SIFS),records an address of a wireless station to perform next response in areceiving address (RA) field, newly forms a multi-user ID list excludingthe receiving station, and transmits a response frame. When a wirelessstation receives a response frame having 1 for a token value and Nullfor a multi-user ID list to perform next response, the wireless stationsets up the token value to ‘0’ indicating that the wireless station isthe last user among the multiple users. Then, the wireless stationtransmits a response frame with Null as the multi-user ID list to anaccess point (AP). Accordingly, the access point can be aware of thatall response processes are completely ended.

A response frame of each wireless station in the second embodiment ofthe present invention may perform the same function of a request frameto a wireless station performing next response. Further, transmission ofa (k+1)^(th) response frame may start within a short inter-frame space(SIFS) after receiving a k^(th) response frame without calculating aresponse frame transmission time of a network wireless station.Accordingly, it is effective for time and channel synchronization, andit can be dynamically responded according to the movement of a wirelessstation.

Hereinafter, the second embodiment of the present invention will bedescribed in detail with reference to FIGS. 5 to 7.

FIG. 5 is a diagram illustrating a method for transmitting a responseframe at a plurality of wireless station in accordance with a secondembodiment of the present invention.

Referring to FIG. 5, an access point (AP) transmits a request framethrough enhanced distributed channel access (EDCA). In the request frametransmitted from the access point (AP), an address of a first wirelessstation STA1 is recorded in a receiving address (RA) field, for example,RA=STA1, three identifiers for wireless stations STA2 to STA4 arerecorded in a next multi-user ID list (NID), and 4 is recorded as atoken value (T=4).

The first wireless station STA1 receives the request frame from theaccess point (AP) and transmits a response frame Rsp after a shortinter-frame space (SIFS). In the response frame transmitted from thefirst wireless station, an address of a third receiving station STA3transmitting a next response frame is recorded in a receiving address(RA) field, a token value is reduced by ‘1’ and set up as ‘3’, and themulti-user ID list is formed of the second station STA2 and the fourthstation STA4 by excluding the third station STA3.

The third wireless station STA3 receives the response frame from thefirst wireless station STA1 transmits a response frame (Rsp) after ashort inter-frame space (SIFS). In the response frame transmitted fromthe third wireless station, an address of the second station (STA2)transmitting a next response frame is recorded in the RA field, thetoken value is reduced by ‘1’ and set up as ‘2’, and the next multi-userID list is formed of the fourth station STA4.

The second wireless station (STA2) receives the response frame from thethird wireless station STA3 and transmits a response frame Rsp after ashort inter-frame space (SIFS). In the response frame transmitted fromthe second wireless station (STA2), an address of the fourth station(STA4) transmitting a next response frame is recorded in the RA field,the token value is reduced by ‘1’ and set up as ‘1’, and the nextmulti-user ID list is setup as null.

The fourth wireless station STA4 receives the response frame from thesecond wireless station STA2 and transmits a response frame Rsp after ashort inter-frame space (SIFS). In the response frame transmitted fromthe fourth wireless station, an address of an access point is recordedin the RA field, the token value is reduced by ‘1’ and set up as ‘0’,and the next multi-user ID list is recorded as ‘null’.

The access point (AP) receives the response frame from the fourthwireless station STA4. The access point (AP) recognizes that response iscompletely ended for all stations because the token value is setup as‘0’ and the next multi-user ID list is setup as ‘null’.

In the second embodiment of the present invention, the request frame andthe response frame are substantially exchanged among wireless stations.Accordingly, transmission failure can be dynamically processed in thesecond embodiment of the present invention.

FIGS. 6 and 7 are diagrams illustrating a method for processingtransmission failure of a response frame. FIGS. 6 and 7 show responsefailure occurred in a second wireless station STA2.

Referring to FIG. 6, the third wireless station STA3 records an addressof the second station STA2 in a RA field after a short inter-frame space(SIFS), sets up a token value as ‘2’ by reducing it by ‘1’, and recordsthe fourth station STA1 at the next multi-user ID list. Then, the thirdwireless station STA3 transmits the response frame.

When the second wireless station STA2 receiving the response frame fromthe third wireless station STA3 fails to transmit a response frame, allwireless stations including access points can be aware of thetransmission failure of a response frame through monitoring a responseframe.

Accordingly, the third wireless station STA3 records an address of thefourth wireless terminal STA4 in the RA field after a short inter-framespace (SIFS) after receiving a response frame of the second wirelessstation (STA2), sets up the token value as ‘2’, sets up the nextmulti-user ID list as ‘null’, and transmits the response frame.

The fourth wireless station STA4 receives the response frame from thethird wireless station STA3. Then, the fourth wireless station STA4records an address of an access point (AP) in the RA field after a shortinter-frame space (SIFS), sets up the token value as ‘1’ by reducing itby ‘1’, sets up the next multi-user ID list as ‘null’, and transmits theresponse frame.

The access point (AP) receives the response frame from the fourthwireless station STA4. Then, the access point (AP) transmits a requestframe as an address of the second wireless station STA2 recorded in a RAfield, which recognized as response frame transmission failure in themonitoring procedure. Accordingly, the second station STA2 transmits aresponse frame.

FIG. 7 is a diagram illustrating a recovery procedure for a transmissionfailure in a method for transmitting a response frame in accordance witha second embodiment of the present invention.

Referring to FIG. 7, the third wireless station STA3 records an addressof the second wireless station STA2 in the RA field after a shortinter-frame space (SIFS), sets up a token value as ‘2’ by reducing it by‘1’, records the fourth wireless station STA4 in the next multi-user IDlist.

When the second wireless station STA2 fails to transmit a response frameafter receiving the response frame from the third wireless station STA3,all wireless stations including an access point can detect the responseframe transmission failure through monitoring the response frame.

Accordingly, the third wireless station STA3 receives the response framefrom the second wireless station STA2, records an address of the fourthwireless station STA4 in the RA field after a short inter-frame space(SIFS), sets up a token value as ‘2’, sets up the next multi-user IDlist as the second wireless station STA2, and transmits a responseframe.

The fourth wireless station STA4 receives the response frame from thethird wireless station STA3, records an address of the second wirelessstation STA2 in a RA field after a short inter-frame space (SIFS), setsup a token value as ‘1’ by reducing it by ‘1’, sets up the nextmulti-user ID list as ‘null’, and transmits the response frame. Thesecond wireless station STA2 receives the response frame from the fourthwireless station STA4, records an address of the access point (AP) inthe RA field after a short inter-frame space (SIFS), sets up a tokenvalue as ‘0’ by reducing it by ‘1’, sets up the next multi-user ID listas ‘null’, and transmits the response frame.

The Access point receives the response frame from the second wirelessstation STA2 and recognizes that all wireless stations completelyrespond because the token value is ‘0’ and the next multi-user ID listis ‘null’.

Since the response frame shown in FIG. 7 may perform a function as arequest frame for a next frame, a recovery procedure among wirelessstations can be performed based on the response frame shown in FIG. 7.Also, the access point (AP) can monitor and manage such a procedure ifthe recovery procedure is delayed and has a problem among wirelessstations.

Hereinafter, a method for exchanging a request frame and a responseframe in accordance with a third embodiment of the present inventionwill be described with reference to FIGS. 8 and 9.

In the third embodiment of the present invention, all multi-userstations do not respond to a multi-request frame. A station transmittinga request frame designates predetermined stations and the designatedstations transmit a response frame.

For example, a RTS/CTS control frame may reserve a wireless channelwithout collision through network allocation vector (NAV) setup for along time such as a frame longer than a transmission request threshold(dot11RTSThreshold) or a transmission opportunity (TXOP).

In the third embodiment of the present invention, all multi-userstations do not transmit a response frame such as a CTS frame or an ACKframe when a RTS frame and a CTS frame are exchanged or when short dataor an ACK frame therefor is exchanged. Only representative wirelessstation responses to the request frame to sense collision or perform afunction of NAV setup.

FIG. 8 illustrates a sixth wireless station STAG designated as arepresentative station to transmit a response frame in accordance with athird embodiment of the present invention.

Referring to FIG. 8, the access point (AP) selects a representativewireless station to transmit a response frame from a plurality ofstations in consideration of various wireless environment factors suchas a channel quality. For example, a wireless station in the worstwireless environment may be selected as the representative wirelessstation from a plurality of wireless stations using channel information.Further, a wireless station that previously failed to respond isdetermined as a wireless station in the worst wireless environment andselected as a representative wireless station.

Referring to FIG. 8, a sixth wireless station STA6 is a wireless channelfarthest from an access point. The sixth wireless station STA6 isselected as a wireless station to transmit a response frame. The sixthwireless station STA6 selects a high reliable modulation and codingscheme (MCS) to safely transfer a response frame to the access point(AP). Accordingly, a plurality of wireless stations receiving theresponse frame from the sixth station STA6 can be aware of channel useinformation.

The access point (AP) receiving a response frame can transmit amultiuser data frame by performing long NVA setup for transmitting data.Accordingly, better performance can be obtained through MU-MIMOtechnology by reducing overhead of receiving a response frame from allwireless stations and obtaining a use right for a channel.

FIG. 9 is a diagram illustrating a method for transmitting a frame usinga representative wireless station designated to transmit a responseframe in accordance with an embodiment of the present invention.

Referring to FIG. 9, a second wireless station STA2 may receive allframes from an access point and a sixth wireless station designated as arepresentative wireless station. Such a second wireless station STA2 canupdate NAV by receiving a request frame and a response frame. Thewireless stations STA1 and STA4 perform a channel NAV setup process by arequest frame transmitted from the access point. The third wirelessstation STA3 may setup a channel NAV using a representative responseframe received from the sixth wireless station STA6.

In FIG. 9, an address of a station receiving a request frame transmittedfrom the access point (AP) is set up as an address of a sixth stationSTA6 which is a representative station to transmit a response frame. Asdescribed above, the request frame can support comparability because therequest frame maintains an existing frame format without modification.Meanwhile, when data transmission is performed at the same time using aMU-MIMO technology, and when a request frame requires information onmulti-user stations, a response frame may include information on thenumber of multi-user stations and a multi-user ID list as described inFIG. 3.

In FIG. 9, if an access point (AP) fails to transmit a response framedue to a response frame time out, the access point (AP) retransmits arequest frame by selecting other wireless station as a representativewireless station to transmit a response frame or retries thetransmission of the sixth station STAG.

The embodiments of the present invention were described to be applied tothe immediate response scheme. However, the embodiments of the presentinvention may be applied to a delayed response scheme that transmits anACK frame at a time of transmitting an immediate response frame fromeach wireless station and transmits a response frame for the requestframe through channel access.

For example, the embodiments of the present invention can be applied towhen a station does not receive a response frame having requestinformation on a predetermined request frame not designated as a CTSframe for a RTS frame or an ACK frame for data. In case of the firstembodiment of the present invention, a multi-user station receiving anACK frame at a transmission time of a response frame individuallytransmits a response frame for a request frame through basic channelaccess.

Since a response frame can be a request frame for a next wirelessstation in case of the second embodiment of the present invention, anACK frame does not include information requested by a request frame.However, the response frame includes a MAC address value of a nextmulti-user station in a receiving address (RA) field and a nextmulti-user station list to perform a response procedure after a tokenvalue. When the access point receives a legacy ACK frame not includingsuch request information, the access point (AP) regenerates andretransmits a request frame for next multi-user stations to perform aresponse procedure after the multi-user station transmitting the ACKframe.

Meanwhile, the above described method for processing a multiuser framein accordance with an embodiment of the present invention can berealized as a program and stored in a computer-readable recording mediumsuch as CD-ROM, RAM, ROM, floppy disks, hard disks, magneto-opticaldisks, and the likes. Since the process can be easily implemented bythose skilled in the art to which the present invention pertains,further description will not be provided herein.

While the present invention has been described with respect to thespecific embodiments, it will be apparent to those skilled in the artthat various changes and modifications may be made without departingfrom the spirit and scope of the invention as defined in the followingclaims.

1. A method of transmitting a response frame in a wireless communicationsystem, the method comprising: receiving, by a first station, from anaccess point, a request frame for requesting channel information to thefirst station and a second station, the request frame including timeinformation, a first user field identifying the first station and asecond user field identifying the second station; and transmitting, bythe first station, to an access point, a response frame as a response tothe request frame, wherein the time information is determined based on asum of an estimated time required for the first station to transmit theresponse frame plus at least one Short Interframe Space (SIFS), andwherein the request frame sequentially includes the time information,the first user field and the second user field.
 2. The method of claim1, wherein the first user field includes an association identifier (AID)of the first station and the second user field includes an AID of thesecond station.
 3. The method of claim 1, wherein the time informationincludes a duration field.
 4. A device for transmitting a response framein a wireless local area network, the device comprising a processorconfigured to: receive, from an access point, a request frame forrequesting channel information to the first station and a secondstation, the request frame including time information, a first userfield identifying the device and a second user field identifying thesecond station; and transmit, to an access point, a response frame as aresponse to the request frame, wherein the time information isdetermined based on a sum of an estimated time required for the deviceto transmit the response frame plus at least one Short Interframe Space(SIFS), and wherein the request frame sequentially includes the timeinformation, the first user field and the second user field.
 5. Thedevice of claim 4, wherein the first user field includes an associationidentifier (AID) of the device and the second user field includes an AIDof the second station.
 6. The device of claim 4, wherein the timeinformation includes a duration field.